NCP5010
http://onsemi.com
11
Finally an acceptable DCR must be selected regarding
losses in the coil and must be lower than 1.4 W to limit
excessive voltage drop. In addition, as DCR is reduced,
overall efficiency will improve. Some recommended
inductors include but are not limited to:
TDK VLF4012AT−220MR51
TDK VLP4612T−220MR34
TDK VLP5610T−220MR45
Coilcraft LPO6610−223M
Coilcraft DO1605T−223MX
Coilcraft DT1608C−223
Capacitor Selection
To minimize the output ripple, a low ESR multi−layer
ceramic capacitor type X5R or equivalent should be
selected. For LED driver applications a 1 mF (min) 25 V is
adequate. The NCP5010 can be operated in a voltage mode
configuration (see Figure 34) for applications such as
OLED power. Under these conditions, C
OUT
can be
increased to 2.2 mF, 25 V or more to reduce the output
ripple.
The input needs to be bypassed by a X5R or an equivalent
low ESR ceramic capacitor near the V
IN
pin. A 1 mF, 6.3 V
is enough for most applications. However, if the connection
between V
IN
and the battery is too long then a 4.7 mF or
higher ceramic capacitor may be needed. Some
recommended capacitors include but are not limited to:
TDK C1608X5R1E105MT
TDK C2012X5R1E105MT
TDK C1608X5R0J105MT
TDK C2012X5R1E225MT
Murata GRM185R61A105KE36D
Murata GRM188R60J475KE19D
Murata GRM216R61E105KA12D
Short−Circuit Protection
If V
OUT
is falls below 50% of V
IN
then a short−circuit
condition is detected. When this event is detected, the
PWM circuitry is disabled and the NMOS power switch is
not turned on. Power will be supplied to the load through
the inductor, rectifier and high side switch. Once V
OUT
reaches 66% of V
IN
, then the PWM circuitry is enabled. In
normal conditions when the device is enabled by an active
high signal on CTRL, the short circuit condition continues
until the output capacitor is charged by the limited current
up to 66% of V
IN
.
Normal
Running
Short−Circuit Condition
Current limited at 20mA
Converter in Standby
End of Short−Circuit
Detected Converter
Starts Again
SC
Occurs
T
Figure 27. Example of the V
OUT
Voltage Behavior
When Short−Circuit Arises
V
OUT
2/3 V
IN
1/2 V
IN
Overvoltage Protection (OVP)
If there is an open load condition such as a loose
connection to the White LED string, the converter will
provide current to the C
out
capacitor and the voltage at the
output will rise rapidly. This could cause damage to the part
if there was not some external clamping Zener clamping
circuit. To eliminate the need for these external
components, the NCP5010 incorporates an OVP circuit
which monitors the output voltage with a resistive divider
network and a comparator and voltage reference. If the
output reaches 22 V (nominal), the OVP circuit will detect
a fault and inhibit PWM operation. This comparator has
1 V of hysteresis so when the load is reconnected and the
voltage drops below 21 V, the PWM operation will resume
automatically. The 22 V OVP threshold allows the use of
25 V ceramic capacitors for the output filter capacitor.
Undervoltage Lock Out (UVLO)
To ensure proper operation under all conditions, the
device has a built−in undervoltage lock out (UVLO)
circuit. During power−up, the device will remain disabled
until the input voltage exceeds 2.4 V nominal. This circuit
has 200 mV of hysteresis to provide noise immunity to
transient conditions.
